Discharge head for a vertical pump and vertical pump

ABSTRACT

A discharge head for a vertical pump includes a base plate configured to mount the discharge head, a top plate, at least one support member connecting the base plate with the top plate, a discharge pipe with an outlet configured to deliver a fluid, and an inner tube. The discharge pipe extends through the base plate. The inner tube is configured to receive a shaft that connects a drive unit with an impeller of the vertical pump, and extends in an axial direction and coaxially within the discharge pipe in a region of the base plate, passing through a wall of the discharge pipe at an intersection, and further extending to the top plate. The inner tube includes a bellows member disposed between the intersection and the top plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit to U.S. Application No. 62/206,529, filed Aug. 18, 2015, the contents of which is hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

The invention relates to a discharge head for a vertical pump.

Background of the Invention

Vertical pumps have been used successfully in a plurality of applications for a very long time. Vertical pumps for specific applications are quite often manufactured in accordance with the specifications of the users or are matched in detail to specific requirements. Vertical pumps may be designed both as single stage and multistage pumps. They are typically immersed into the liquid reservoir to be pumped, so that at least the intake or suction bell with the adjoining pump rotor is immersed into the fluid to be pumped, so that the pump is directly ready for operation.

SUMMARY

One field of increasing importance for the use of vertical pumps is the energy generation with solar energy systems, especially with concentrated solar power (CSP) systems. These systems use mirrors or lenses to concentrate the sunlight collected by a large area onto a small area, where the sunlight heats a heat transfer fluid (HTF) which is used for example to generate steam for driving a turbine for an electric power generator. Nowadays, one of the preferred heat transfer or heat storage fluids is molten salt.

A typical setup of such a CSP system comprises a plurality of solar collectors which concentrate the sunlight to the top of a central tower. There are at least two tanks for the molten salt, namely a cold tank and a hot tank. The molten salt in the cold tank has for example a temperature of up to 350° C. The molten salt is pumped from the cold tank to the top of the central tower where it is heated by the sunlight and then moved to the hot tank in which the molten salt typically has a temperature of up to 600° C. The molten salt in the hot tank may be stored, if necessary, for up to several days without an essential loss of the stored heat. For generating the electric power the molten salt is moved from the hot tank for example to a steam generator that transfers the heat from the molten salt to water in order to generate steam which in turn drives a steam turbine connected to a generator to produce electric energy. The molten salt is returned from the steam generator to the cold tank.

For conveying the molten salt in such a CSP system vertical pumps are used which are mounted to the cover of a tank and extend downwardly into the molten salt. A typical setup of a vertical pump comprises a pumping unit with an inlet and an impeller for conveying the molten salt and being immersed into the reservoir of molten salt. The pumping unit is usually connected to the cover of the tank or to a supporting structure at the tank, such that the impeller may be immersed into the molten salt in the tank. On top of the cover of the tank the discharge head of the vertical pump is mounted having an outlet for the fluid, i.e. the molten salt. On top of the discharge head an axial bearing unit for the drive shaft is provided as well as a drive unit for driving the impeller. The drive unit is operatively connected to the impeller by the drive shaft extending within a tube being arranged between the discharge head and the impeller.

The high temperature and the properties of the molten salt are a big challenge regarding an appropriate design of the vertical pump. To address environmental, safety and maintenance issues vertical pumps for molten salt are usually designed as sealless pumps. A sealless pump does not use packing or mechanical seals to prevent the process fluid, e.g. the molten salt, from escaping to the environment but other methods which are known in the art, for example the use of sealing fluids. Thus, in a sealless vertical pump there is no packing and no mechanical seal that shall get into contact with the molten salt.

Another challenge is the considerable thermal stress which is due to the high temperature of the molten salt of up to 600° C. as compared to ambient temperature and thermal transients. Usually, the vertical pump in a tank for molten salt does not discharge the molten salt continuously but has duty cycles depending inter alia from the availability of sunlight. Thus, it may be that the vertical pump runs at idle for several hours so that the pump head cools down by losing heat to the environment. Then, the restart of the pump results in a thermal shock of the discharge head. On the other hand, during operation when the components of the pump are in thermal equilibrium with the molten salt large temperature gradients arise on those parts of the pump which are both exposed to the temperature of the molten salt and to ambient temperature. These effects cause a considerable thermal load on the components of a vertical pump.

The invention addresses these problems which are due to the high temperature differences between a fluid conveyed by a vertical pump and the environment of the vertical pump. Therefore, it is an object of the invention to propose a new discharge head for a vertical pump and a vertical pump that are in particular suited for conveying a fluid having a temperature which is considerably different from ambient temperature. Especially, the discharge head and the vertical pump shall be suited for conveying very hot fluids like molten salt of up to 600° C.

The subject matter of the invention satisfying this object is characterized by the features disclosed herein.

Thus, according to the invention a discharge head for a vertical pump is proposed comprising a base plate for mounting the discharge head, a top plate, at least one support member connecting the base plate with the top plate, a discharge pipe with an outlet for delivering a fluid, said discharge pipe extending through the base plate, and an inner tube for receiving a shaft that connects a drive unit with an impeller of the vertical pump, wherein the inner tube extends in an axial direction and coaxially within the discharge pipe in the region of the base plate, passes through a wall of the discharge pipe at an intersection, and further extends to the top plate, wherein the inner tube comprises a bellows member being located between the intersection and the top plate.

The invention is in particular based upon the finding that especially the section of the inner tube between the intersection where the inner tube passes through the wall of the discharge pipe and the connection of the inner tube to the top plate is exposed to very high thermal stress that can result in a bending of the inner tube. This bending places a significant strain both on the connection of the inner tube with the discharge pipe and on the connection of the inner tube with the top plate. In addition, the bending may also result in a deformation of other components like the base plate, the top plate and the support member. This strain is considerably released by providing the bellows member between the intersection and the top plate. It is one of the effects of the bellows member that it compensates different thermal expansions of the components and thus considerably reduces the high stresses is the discharge head due to temperature differences and thermal transients. It is found that the discharge head according to the invention has a clearly improved life time even when subjected to a large number of thermal cycles resulting from the change from an idle operation of the pump to a conveying operation and vice versa.

According to a preferred embodiment the bellows member is firmly connected to the top plate, for example by welding.

Advantageously, the bellows member extends over at least half the distance between the intersection and the top plate because this enables a very good compensation of the different thermal expansions.

Furthermore, it is found favorable for the reduction of the thermal stress, when the discharge pipe has a vertical section extending in the axial direction, a horizontal section extending perpendicular to the vertical direction and an intermediate section connecting the vertical section with the horizontal section.

From a constructional point of view it is preferred that the intermediate section extends at an angle of approximately 45° with respect to the axial direction.

It is a further preferred measure for reducing the thermal stress that the at least one support member has a main extension being in a plane that is parallel to the axial direction. It becomes apparent that this orientation of the support member is more favorable with respect to the thermal behavior than a radial orientation where the support member extends in a radial direction, i.e. perpendicular to the axial direction.

To provide a stronger and uniform support for the top plate embodiments are preferred having a plurality of support members, wherein each support member has a main extension being in a plane that is parallel to the axial direction.

Still a further advantageous measure for reducing the thermal stress is to provide a discharge support for the discharge pipe, which is firmly connected to the base plate, and which has a main extension being in a plane that is parallel to the axial direction.

Preferably, the discharge support has no contact with the top plate to avoid a direct heat transfer between the top plate and the discharge support.

Even more preferred to reduce the thermal stress, the discharge support is connected only to the base plate and to the horizontal section of the discharge pipe.

According to a preferred embodiment the discharge head has a supply line ending in the inner tube for supplying a sealing medium to the inner tube. By providing a sealing medium to the inner tube it is ensured that the fluid conveyed by the vertical pump cannot pass through the inner tube for example up to a stuffing box or an axial bearing.

In addition, the invention proposes a vertical pump for conveying a fluid comprising a pumping unit with an inlet and an impeller for conveying the fluid, a discharge head with an outlet for the fluid, a drive unit for rotating the impeller, a shaft extending in an axial direction and connecting the drive unit with the impeller, wherein the discharge head is designed according to the invention.

In a preferred embodiment the vertical pump has an axial bearing unit with an axial bearing for the shaft, wherein the axial bearing unit is mounted to the top plate of the discharge head, and wherein the motor unit is mounted to the axial bearing unit.

Due to the discharge head being designed according to the invention the vertical pump is preferably designed for conveying a hot fluid of at least 250° C., in particular for conveying a molten salt.

According to a preferred application the vertical pump is designed and adapted to be mounted to a tank for a molten salt in a solar energy system or to a support structure at the tank. The support structure is designed in such a manner that the vertical pump may be mounted above the tank with the shaft of the vertical pump extending into the tank.

Further advantageous measures and embodiments of the invention will become apparent from the description herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail hereinafter with reference to the drawings.

FIG. 1 is a perspective cross-sectional view of an embodiment of a discharge head according to the invention,

FIG. 2 is a cross-sectional view of an embodiment of a vertical pump according to the invention,

FIG. 3 is an enlarged cross sectional view of the discharge head of the vertical pump shown in FIG. 2, and

FIG. 4 is a top view of the discharge head of the vertical pump shown in FIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the drawings respective identical parts or parts having the same function or an analogously same function are designated with the same reference numerals.

FIG. 1 shows a perspective, cross-sectional view of an embodiment of a discharge head for a vertical pump according to the invention. The discharge head is designated in its entity with reference numeral 10. FIG. 2 shows a cross-sectional view of an embodiment of a vertical pump according to the invention being designated in its entity with reference numeral 1 and comprising a discharge head 10 according to the invention.

In the following description reference is made by way of example to the important application that the vertical pump is designed and adapted for a solar energy system which is a concentrated solar power (CSP) system using molten salt as the heat transfer fluid (HTF) or as the heat storage fluid, respectively. More particular, in this example the vertical pump is mounted to a tank for molten salt, e.g. to a cover of the tank, and conveys the molten salt from the tank to other locations of the concentrated solar power system. Of course, the vertical pump may also be mounted to a support structure at the tank, especially to a support structure that is located above the tank, such that the vertical pump may be mounted above the tank for extending into the tank.

It goes without saying that the invention is not restricted to this example but may be used in a lot of different applications, especially in such applications where a vertical pump is used for conveying a fluid having a temperature which is considerably different from ambient temperature. Especially, the discharge head and the vertical pump according to the invention is suited for conveying very hot fluids like molten salt of up to 600° C. and even more.

Since vertical pumps as such are very well known from the prior art in the following description only those components are described in more detail which are essential for the understanding of the invention.

The embodiment of the discharge head 10 for a vertical pump illustrated in FIG. 1 comprises a base plate 11 for mounting the discharge head 10 for example to a cover 101 (see FIG. 2) of a tank 100 for molten salt and a top plate 12 which is designed as a circular disk being parallel to the base plate 11. At least one support member 13 connects the base plate 11 with the top plate 12 providing support for the top plate 12. In this embodiment of the discharge head 10 a plurality, namely three, support member 13 are provided two of which are represented in FIG. 1.

The discharge head 10 further comprises a discharge pipe 15 with an outlet 16 for discharging a fluid, here the molten salt from the tank 100. The discharge pipe 15 extends through the base plate 11 and has a mitered design comprising a vertical section 151 extending in a vertical direction through the base plate 11, a horizontal section 152 extending perpendicular to the vertical section 151 between the base plate 11 and the top plate 12, as well as an intermediate section 153 connecting the vertical section 151 with the horizontal section 152. The outlet 16 is located at the end of the horizontal section 152.

In addition, the discharge head 10 comprises an inner tube 17 for receiving a shaft 4 (see FIG. 2) that connects a drive unit 3 with an impeller 21 of the vertical pump 1. The inner tube 17 extends in an axial direction A which is defined as the axis of rotation around which the impeller 21 rotates during operation. In the usual operating position of the vertical pump 1, i.e. in a vertical orientation, which is shown in FIG. 2 the axial direction A coincides with the vertical direction. Hereinafter relative terms regarding the location like “above” or “below” as well as the terms “horizontal” and “vertical” refer to this operating position shown in FIG. 2.

The inner tube 17 extends in the axial direction A and coaxially within the vertical section 151 of the discharge pipe 15 in the region of the base plate 11. At an intersection 18 the inner tube 17 passes through a wall of the discharge pipe 15, further extends in the axial direction A to the top plate 12 and crosses the top plate 12 in its center. The inner tube 17 is firmly connected to the top plate 12, for example by way of welding. In addition, at the intersection 18 the inner tube 17 is firmly connected to the discharge pipe, preferably by welding. Below the base plate lithe inner tube 17 is provided with two return lines 20 each of which branches off from the inner tube 17 essentially perpendicular to the axial direction A. Each return line 20 extends first perpendicular to the axial direction and is then curved downwardly into the axial direction A. The function of the return lines 20 is to return the leakage flow of the molten salt flowing upwardly in the inner tube 17 back to the tank 100.

The intersection 18 of the inner tube 17 with the discharge pipe 15 is located in the intermediate section 153 of the discharge pipe. The intermediate section 153 extends at an angle of approximately 45° with respect to the axial direction A between the vertical 151 and the horizontal section 152 of the discharge pipe 15.

According to the invention the inner tube 17 comprises a bellows member 19 which is located between the intersection 18 and the top plate 12. By the bellows member 19 the inner tube 17 is able to change its extension in the axial direction A between the intersection 18 and the top plate 12. This allows for a compensation of the different thermal expansions of the components like the inner tube 17, the discharge pipe 15 or the top plate 12 thus considerably reducing the thermal stress that occurs in the discharge head 10 during operation. During operation the discharge head 10 is exposed to very strong thermal shocks, for example when changing the vertical pump 1 from an idle operation, in which no molten salt is discharged to a conveying operation in which the molten salt is discharged through the discharge pipe 15. In addition, the discharge head 10 is exposed to large temperature gradients during operation because on the one side the hot molten salt having temperatures up to 600° C. or even more flows through the discharge pipe 15 also contacting the inner tube 17 and on the other side the inner tube 17, the base plate 11 and the top plate 12 are exposed to the ambient temperature outside the tank 100. By allowing the inner tube 17 to change its length in axial direction it may be successfully avoided that the inner tube 17 is subject to a bending or a partial displacement in radial direction, i.e. perpendicular to the axial direction A. Such bending would also impose additional stress especially on the intersection 18 an in addition to the top plate 12 and the support members 13.

Preferably the bellows member 19 is fixed to the top plate 12. This may be done by way of welding or any other method suited to provide a firm connection of the bellows member 19 with the top plate 12. The bellows member 19 which forms a part of the wall of the inner tube 17 is preferably made of a metallic material, e.g. an alloy suited for the high temperatures occurring in the inner tube 17. Suited materials for the bellows member 19 are known in the art and comprise for example steel like an austenitic steel.

In order to enable a particularly effective compensation of different thermal expansions the bellows member 19 has a length L (see FIG. 3) in the axial direction A that is at least half the distance between the intersection 18 and the top plate 13. The bellows member 19 can also extend—as shown in FIG. 1 and FIG. 3 nearly over the entire distance between the bottom face of the top plate 12 and the intersection 18 as far as it is possible from the constructional point of view.

A further preferred measure to reduce the thermal stress in the discharge head 10 is the orientation of the support members 13. As it can be seen in FIG. 1 and FIG. 4 each support member 13 has a main extension E being in a plane that is parallel to and spaced with respect to the axial direction A. Thus, as can be seen best in FIG. 4 each support member 13 is arranged in a circumferential orientation with respect to the vertical section 151 of the discharge pipe 15 rather than in a radial orientation.

There are three essentially identical support members 13 (see FIG. 4) each of which connects the base plate 11 with the top plate 12 and each of which has a circumferential orientation with respect to the vertical section 151 of the discharge pipe 15, i.e. each of the support members 13 has a main extension E in a plane that is parallel to the axial direction A and spaced from the axis of rotation of the shaft 4.

Preferably the support members 13 are equidistantly arranged around the inner pipe 17 (or the vertical section 151 of the discharge pipe 15) in order to provide a strong and uniform support for the top plate 12. As the top plate 12 may be used as stand for the axial bearing and/or the drive unit 3 of the vertical pump 1 it has to carry a considerable load and therefore needs a reliable support.

By the circumferential orientation of the support members 13 the heat transfer between components that are exposed to strongly different temperatures during operation of the pump 1 is reduced which also results in a reduction of the thermal stresses.

The discharge head 10 further comprises a discharge support 14 for the discharge pipe 15 which is firmly connected to the base plate 11 and which provides support to the horizontal section 152 of the discharge pipe 15. The discharge support 14 is designed as a plate-like member having a central opening for receiving the discharge pipe 15 and for closely fitting around the entire circumference of the discharge pipe. This may be achieved for example by welding the discharge support 14 to the discharge pipe 15 or by designing the discharge support as a two part member, whereas the two parts are fixed to each other by screws or bolts thus providing a firm connection between the discharge support 14 and the discharge pipe.

Like the support members 13, the plate-like discharge support 14 also has a circumferential orientation with respect to the inner tube 17, i.e. it has a main extension in a plane that is parallel to the axial direction A. In order to minimize the heat transfer between components of the discharge head 10 it is preferred, that the discharge support 14 has no contact with the top plate 12. This may be realized by locating the discharge support 14 at a distance from the axis of rotation of the shaft 4 that is larger than the diameter of the top plate 12. Mostly preferred the discharge support 14 is connected only to the base plate 11 and to the horizontal section 152 of the discharge pipe 15 but to no other components of the discharge head.

As already said, FIG. 2 shows a cross-sectional view of an embodiment of the vertical pump 1 according to the invention comprising a discharge head 10 according to the invention. The discharge head 10 may be designed as described hereinbefore. The reference numerals in FIG. 2-FIG. 4 have the same meaning as already explained.

FIG. 3 shows an enlarged cross sectional view of the discharge head 10 of the vertical pump 1 in FIG. 2 and FIG. 4 shows a top view of the discharge head 10 of the vertical pump 1 shown in FIG. 3.

The vertical pump 1 for conveying a fluid, for example molten salt, comprises a pumping unit 2 with an inlet 22 for the molten salt and at least one impeller 21 for conveying the molten salt. The vertical pump 1 may be designed as a single stage pump with only one impeller 21 or as a multistage pump 1, in which the pumping unit 2 comprises several impellers 21 being arranged one behind the other with respect to the axial direction A. In the embodiment according to FIG. 2 the vertical pump 1 is designed as a multistage pump 1 having six impellers 21.

The vertical pump 1 further comprises the discharge head 10 with the outlet 16 for the molten salt, the drive unit 3 for driving the impellers 21 of the pumping unit 2, the shaft 4, also referred to as line shaft, that operatively connects the drive unit 3 with the impellers 21 for rotating the impellers 21 The shaft 4 may be a single part or it may consist of two or more shaft pieces which are connected by one or more couplings.

The vertical pump 1 is mounted to the tank 100 for the molten salt. The tank 100 as well as its cover 101 are only symbolically indicated in FIG. 2.

The mounting may be performed in the following way: The pumping unit 2 with the impellers 21 is mounted for example by way of screws or bolts to the inner face of the cover 101 of the tank 100 and is freely hanging down from there to the inside of the tank 100. The base plate 11 of the discharge head 10 is mounted to the outer face of the cover 101 of the tank 100. It is possible that the base plate 11 is a separate part which is mounted to the cover 101 by bolts or screws being received by screw holes 23 (see FIG. 4) The cover 101 may be a separate part or it may be an integral part of the tank 100.

Thus, the discharge head 10 of the vertical pump 1 is located outside the tank 100 and the pumping unit 2 is located inside the tank 100, such that the inlet 22 of the pumping unit is immersed in the molten salt during operation.

The discharge pipe 15 of the discharge head 10 is connected to an outlet pipe 7—also referred to as column—extending in axial direction and being in fluid communication with the outlet of the last impeller 22. The connection between the discharge pipe and the outlet pipe 7 may be realized by screws or bolts. The inner tube 17 of the discharge head 10 extends within the vertical section 151 of the discharge pipe 15 and surrounds the shaft 4. The inner tube 17 ends below the orifices of the return lines 20.

The vertical pump 1 further comprises an axial bearing unit 6 with at least one axial bearing 61 for journaling the shaft 4 with respect to the axial direction. The axial bearing unit 6 is mounted to and supported by the top plate 12 of the discharge head 10. The top plate 12 comprises a stuffing box 62 for the lead through of the shaft 4 from the discharge head 10 to the axial bearing unit 6. The stuffing box 62 is designed in a manner being as such known in the art.

The drive unit 3, for example an electric motor, is mounted on top of the axial bearing unit.

The vertical pump 1 is designed as a so-called sealless pump. A sealless pump does not use packing or mechanical seals to prevent the process fluid, i.e. the molten salt, from escaping to the environment but other methods which are known in the art, for example the use of sealing fluids. Thus, in a sealless vertical pump there is no packing and no mechanical seal that shall get into contact with the molten salt. To avoid any contact for example of the stuffing box 62 or the axial bearing 61 with the molten salt, the inner tube 17 comprises the two return lines 20 already described hereinbefore to return any leakage flow of the molten salt upwardly along the shaft 4 to the tank 100.

In addition, the discharge head 10 comprises a supply line 24 ending in the inner tube 17 for supplying a sealing medium, for example nitrogen gas, to the inner tube 17. As best seen in FIG. 2 and FIG. 3 the orifice where the supply line 24 ends in the inner tube 17 is located between the intersection 18 where the inner tube 17 passes through the wall of the discharge pipe 15 and the bellows member 19 of the inner tube 17. The supply line 24 may be connected with a reservoir for a sealing fluid delivering the sealing fluid to the inner tube. The sealing fluid enters the inner tube 17 and blocks the passage upstream of the return lines 20 for the molten salt. Thus, any leakage flow of the molten salt upwardly along the shaft 4 is forced into the return lines 20. In case of nitrogen gas as sealing medium or sealing fluid the nitrogen is supplied to the inner tube 17 by the supply line 24 with a pressure that is high enough to prevent the molten salt from reaching the inner tube 17.

During operation of the vertical pump 1 the molten salt in the tank 100 enters the pumping unit 2 by the inlet 22 at the downside end of the vertical pump and is conveyed by the impellers 21 through the outlet into the outlet pipe 7 and then through the discharge pipe 15 of the discharge head 10 to the outlet 16. The outlet 16 is connected with a pipe (not shown) guiding the molten salt to the desired location.

In order to reduce the thermal load or the thermal stress in the discharge head 10 of the vertical pump 1 it is also possible to dispense with the bellows member 19 and to provide only the support members 13 in a manner described hereinbefore or only the discharge support 14 in a manner described hereinbefore or a combination of the support members 13 and the discharge support 14 as described hereinbefore. 

1. A discharge head for a vertical pump, comprising: a base plate configured to mount the discharge head; a top plate; at least one support member connecting the base plate with the top plate; a discharge pipe with an outlet configured to deliver a fluid, the discharge pipe extending through the base plate; and an inner tube configured to receive a shaft that connects a drive unit with an impeller of the vertical pump, the inner tube extending in an axial direction and coaxially within the discharge pipe in a region of the base plate, passing through a wall of the discharge pipe at an intersection, and further extending to the top plate, the inner tube comprising a bellows member disposed between the intersection and the top plate.
 2. A discharge head in accordance with claim 1, wherein the bellows member is firmly connected to the top plate.
 3. A discharge head in accordance with claim 1, wherein the bellows member extends over at least half a distance between the intersection and the top plate.
 4. A discharge head in accordance with claim 1, wherein the discharge pipe has a vertical section extending in the axial direction, a horizontal section extending perpendicular to the axial direction and an intermediate section connecting the vertical section with the horizontal section.
 5. A discharge head in accordance with claim 4, wherein the intermediate section extends at an angle of approximately 45° with respect to the axial direction.
 6. A discharge head in accordance with claim 1, wherein the at least one support member has a main extension being in a plane that is parallel to the axial direction.
 7. A discharge head in accordance with claim 1, wherein the at least one support member includes a plurality of support members, and each support member of the plurality of support members has a main extension being in a plane that is parallel to the axial direction.
 8. A discharge head in accordance with claim 1, wherein the discharge pipe includes a discharge support firmly connected to the base plate, discharge support having a main extension being in a plane that is parallel to the axial direction.
 9. A discharge head in accordance with claim 8, wherein the discharge support has no contact with the top plate.
 10. A discharge head in accordance with claim 8, wherein the discharge support is connected only to the base plate and to a horizontal section of the discharge pipe.
 11. A discharge head in accordance with claim 8, further comprising a supply line ending in the inner tube, the supply line being configured to supply a sealing medium to the inner tube.
 12. A vertical pump for conveying a fluid, comprising: a pumping unit with an inlet and an impeller, and configured to convey the fluid; a discharge head in accordance with claim 1; a drive unit configured to rotate the impeller; and a shaft extending in an axial direction and connecting the drive unit with the impeller.
 13. A vertical pump in accordance with claim 12, further comprising an axial bearing unit with an axial bearing for the shaft, the axial bearing unit being mounted to the top plate of the discharge head, and the motor unit being mounted to the axial bearing unit.
 14. A vertical pump in accordance with claim 12, wherein the vertical pump is configured to convey a fluid of at least 250° C.
 15. A vertical pump in accordance with claim 12, wherein the vertical pump is configured to be mounted to at least one of a tank for a molten salt in a solar energy system and to a support structure at the tank.
 16. A vertical pump in accordance with claim 12, wherein the vertical pump is configured to convey a molten salt. 